Magnetron modulator



March 8, 1938.

E. G. LINDER MAGNETRON MODULATOR Filed Jan. 51; less 3 Sheets-Shee't 1Filed Jan. 31, 1936 3 Sheets-Sheet 5 Patented Mar. 8, 1938 UNITED STATESMAGNETRON MODULATOR PATENT OFFICE REISSU'ED Ernest G. Linder,Philadelphia, Pa., assignor to Radio Corporation of America, acorporation of Delaware 7 Claims.

My invention relates to a magnetron modulator. More particularly, myinvention relates to the modulation of magnetrons by moving the anodewith respect to the cathode, or by moving both electrodes with respectto the permanent magnetic field of the magnetron.

A magnetron is a thermionic tube including one or more anodes, acathode, and a magnetic field. The lines of force of the field aresubstantially 10 parallel to the cathode. The electrons from the cathodefollow a curved path 2 which may be illustrated by Figure IA. The curvedor circular path is due to the forces exerted on the electrons by themagnetic field, the anodes 5, l, and the cathode 3.

In contrast to the magnetron, an ordinary triode has a cathode, grid andanode. No magnetic field is required. The electrons travelin asubstantially straight line from the cathode to the anode. The number ofelectrons which reach the anode is normally determined by the spacing ofthe electrodes, and the relative grid, anode and cathode potentials.

I am aware of ordinary electron tubes in which the electrodes have beenrelatively movable. The movement of electrodes in such tubes hasslightly varied the number of electrons reaching the anode, or theamplification factor if a triode is used. In the case of a diode ortriode relatively small movement of the electrodes will have a secondaryeffect on tube operation.

The operation of a magnetron is especially suited to modulation byrelative movement of electrodes or of electrodes with respect to themagnetic field. Since the magnetron is used at ultrahigh frequencies,the capacity between the anodes is of primary importance. Aslightrelative movement will have a very large effect on the operatingfrequency; Furthermore, [the circular path of the electrons makes itpossible to completely stop the flow of electrons to one anode and togreatly increase the electron flow to the other.

Since the electron path is dependent upon the lines of force of thepermanent magnetic field, the operation of the magnetron will be greatlyaffected by a slight relative movement of the electrodes with respect tothe field. By way of example, the effect of moving the anodes withrespect to the cathode is illustrated in Fig. IB and Fig. IC. Othertypes of relative movement will produce large changes in anode current.These changes are due to the characteristic magnetron operation.

One of the objects of my invention is to modu- MAY 2 1 late a magnetronby changing the relative spacing of the cathode and anode electrodes.

Another object is to modulate a magnetron by moving the cathode andanode electrodes with respect to the magnetic field. 5

Another object is to change the relative spacing of the magnetronelectrodes by means of a sound operated diaphragm.

Another object is to vary the operating frequency of a magnetron bymoving its electrodes 10 in a non-uniform field.

A further object is to operate a single magnetron as an oscillator,modulator and 'microphone.

A still further object is to vary the frequency 15 of a magnetronoscillator by varying the interelectrode capacitance; a

An additional object is to provide means whereby a magnetron may be madeto generate audio frequency currents. 20.

Reference is made to the accompanying drawings in which Figure IA,FigureIB, and Figure IC are illustrative of the operation of a magnetronembodying my invention,

Figure II is a schematic diagram of a mag- 25 netron oscillatorincluding modulation means,

Figure III is an illustration of a magnetron modulated by a soundactuated diaphragm,

Figure IV is a schematic diagram of a modification of Figure I, 30

Figure V is a schematic diagram of a-magnetron in which the anodes aremoved with respect to cathode for frequency modulation,

Figure VI is a schematic diagram of a magnetron in which the tube andelectrodes are 35 moved with respect to a magnetic field of nonuniformcharacteristics.

Figure VIa. represents the anodes and the electro-magnet for producingthe non-uniform field of Figure VI, 40

Figure VIb is a plan view of the tube moving means shown in elevation inFigure VI.

Figure We is a, plan view of the pivotal mounting'and biasing springshown in elevation in Figure VI. 45

Figure VII is a schematic diagram of a magnetron similar to Figure VI inwhich the tube moving means is a sound actuated diaphragm,

and

Figure VIII is a modification of the apparatus 50 of Figure VII. 1

Throughout this specification similar reference numerals will be used todesignate similar parts. In Figure II within an evacuated glass envelopel are mounted a cathode 3 and apair of anodes 55 7 line which may be,connected to a dipole antenna I the armature 3|. v magnet is seriallyconnected towalocal battery. a r

Theianodesare connected to a pair of lead wires ll, l3. A conductor 151connects the lead wires. This conductor and the anodes 5, 1 .form aresonant circuit. 1 V

, The lead wires 1 I, [3 may form atransmission or the like; Thenegative terminal .OI-an anode batteryl] is connected to'tlie cathode3.; The positive terminal of the anode battery is connected to abridging conductor I9 which is suitably located on the leads ll,'l3.

A U-shape magnetic core 2| is energized byia' core 23' and abatterySuitable jaws (not g microphone. Instead of modulating. the magshown)are attached to: the pole' pieces'gofythe core 2l to clamp the envelope"I; The magnetic lines offorce between the pole. pieces surround 'and aresubstantially, parallel to the? cathode 3.

The arrangement thus far described may beoperated as a magnetronoscillator. f I -A series of corrugations-11am formed in the section ofthe envelope adjacent the. leadin 'of.

.tlietransmissionwiresill, l3. .A.connecting link 19 is fixed: to the'.end of, the envelope adjacent the corrugations 21; TA"m'agnetic.armature 3l' is fastened to the endiof the link-.29.. Anele'ct'romagnet33 is suitablypositioned with respect 'to Thewinding ofthe electro- 35-and a-microphone 31. J

The corrugations 21 offer;suflicient'iieiribility to the "envelope: I.:to permit movement of the corrugated end of- 'the envelope. with respectto the portion'clamped by the jaws attached to. the

magnetic core 2|; .A slight movement of -.the corrugated en'dwhichalsosupportstheleadwires ll, l3. causes a substa ntial'.mdvement..ofI'theanodes 5, I. with-respect to the cathode]; This movement results =.in.:achange. of electron dis-- tribution-represented by Figs.- IB toIC. ThisI spect'to each other will. s'ubstantlally varytheir change-.willmodulate the normalielectronflow.

. .aWhile. Iihayeiillustrated the.electromagnet. 33,

Q 'and microphone 3-'| -as' a convenient 1 means'of flexing'the tube toefiectmodul'ation, itl fs'hould be understood thatfother. meansxmaybe-employed.= For example,,a 'sound; actuated: dia.-'

1 Dhr'agm,. a mechanicalr'noveinent for'telegraphic' signalling,orainpllflers may beusedi m :Fig. III, the circuit:.is. representative,of a

but of. the device.-

magnetron 1 microphone amplifier; In this de.-

' vice the 'magnetronoperates; asia microphone. and also .as' anamplifier; although .amplifica? tion'is not essential; The leads. I I.,.I3 are 'con.-' nected to-the primary 39: of. the pushepullti ans formerv3|. The anode battery llxis conneeted' to the center tap.ofathe'primary- 39; 1 Theisec: ondary 43 of the transformerrirepresentsthe-but :-.n1 place ofthe s atement motor .dri-iagure II, a soundoperated diaphragm. hasib'een connected to :theLlink H-a .A' movemeht:of; :the'

diaphragm lis transmitted throughthe link 29 to. l

the. flexible end of the envelope; ,Thernove- Y a ment ofJthei-en'velopeinLturn varies the relative:

position of anodes and cathode; 'I'his'alter's" the electrondistribution andnence: the'current flow through..the':primary'39..1Q

i-A modificationof; Eigure II is. mamas FigureIV. Thismodification'consists primarily free end of the metal envelope includesa glass insert '49 through which cathode. leads may be brought. a

In this modification, the cathode is moved with respect-to the anodeelectrodes 5, 'l. The electro-magnetic motor device represented byarmature 3I and magnet. 33 has been connected.

. II may beused in place of the links and lever.

Likewisethe diaphragm 45 of Figure III may be "substituted for theelectromagnetic motor.

The schematic circuit of Figure IV represents" a combined magnetronoscillator, amplifier, and

netroncscinamr the connection of this figure may be arranged'similar toFigure III with a reentirely: rigid- "Instead of flexing theenvelope,

armatures 6|, were fastened'to the lead wires- II. I3," by forces,generated by the.e1ectromagnets'85 ,fl.

The armatures are attracted or repelled Various movements .of the anodesmay be obtained by 'proper'phasing. of the exciting. curre'nts.-The-spaces between the armatures SI; 63 and the walls of the envelopeare sufllcient to permit.free' movement of. the V armatures. Thebridging conductor '59; which :may :be employed in 'ja magnetr'o'noscillator, has sufllcient length andlflexibility to permit movement ofthe" lead wires-J3. 1

Sincethe. anodes 5, I are'attached' to the lead wires, they may bemoved-with respect to each other.,: or with respect -to the: cathode 3;If the magnetron isoscillatingas a negative resistance device,theoscillatory frequency is'inversely pro portional to the capacitybetween the anodesf therefore, the movements of the anodes withrecapacities. and'the oscillatory frequency. Ifthe magnetron isoscillating as an electronic oscillator. variations in relative. anodespacing will vary theamplitude'of oscillations Thus,the magnetronoscillator of' Figure V may be .frequency modulated byimprssingcurrent's 01 the magnets 65, 61. j

The: arrangement: 615.:Figur'e V may ployed as Imicrophone-ampliflerinstead of' an oscillator. As an amplifier, the bridgingconductormaybeomitted. Inboth cases, the'magnetic -fie1d is used. The electro magnetstructure- 2|,

23,;25 :of Figure II.is,suitable for thistpurpose.

. .A. U :shapezpermanent magnet m'ay-be s d a; s how'n-in;Fi'g.lV.. g

desired modulation -frequency on the electro- 2 piste /dot. using heangemem of'Figure it as 'a microphone-amplifier combination, this devicemay. be ,used toi'generateaudio frequency currents. Inthe generationofaudio. frequency currentsijthe. microphone *31 1 isl omitted. A

portion of the output currents, in the 'proper' phase, is fed; back ;to'the ;exciting" .magnets 35,

SLThe feedback currents may :be; amplified "by aetriodeor the. like. Thefrequency of the V audioicurrents can be controlledby'adjusting the inatural frequehcy of vibration. of the anodes 3,-

1 ,'ar matures BI, .63 and lead wires H, l3.

Figure VI. represents, a. magnetron oscillator joramplifier.whichisxmoVediB-S a whole by the modulationjmeans'; Theanodeand cathode el'ectoryfcurrenta-onthe-amplification. depends upon-trodes;. are-.moved through a'non uniform magnetieflfleld. Since'thefrequency of the oscilla the magnetic field strength, modulation will beeffected by the relatively varying field. This arrangement is bestadapted to the electronic mode of oscillation. r

In Figure VI, the envelope I is suitably fastened to a pivot member 'II.The pivot member II is pivotally supported by a yoke member I3. One ormore biasing springs I are connected between fixed studs 11 on the yokeI3 and the pivot member to yieldably position the tube. These biasingsprings may be helical in form similar to the hair spring on a watch.

The electro-magnetic system of this figure differs from the precedingfigures. In the preceding figures, the pole pieces of the core 2| wereof normal uniform shape and produced a substantially uniform field. Thepole pieces I9 for this embodiment of my invention are illustrated inFigure VIII. The effect of the slanting pole pieces 19 is to produce amore dense magnetic field between the near points and less dense betweenthe more widely spaced points. Movement of the anodes 5, I and cathode 3in the non-uniform field will be equivalent to varying the field. Thisvariation modulates the anode current or varies the frequency ofoscillation.

In place of slanting pole pieces, various shape pole pieces may be used..For example, a V or inverted V-shape pole piece or a conical shape willhave the required non-uniform field. Where the field has a rate ofvariation which is uniform with respect to movements on either side ofthe cathode, push-pull modulation may be produced. 1

The non-uniform field may be used for purposes other than modulation.For example, a permanent magnet may be substituted for the electricalone and the operating frequency of the magnetron varied by moving themagnet with respect to cathode and anode. Such a system lends itselftoportability and simplicity of frequency adjustments.

One means for moving the magnetron of Figure VI is illustrated as anelectro-magnetic driver 8I. The driver is shown in plan view in FigureVI and in elevational view in Figure VIb. A pair of arms 83 are rigidlysecured to the envelope I. A magnetic armature 85 is secured to the endsof these arms by soldering, welding or the like.

The biasing springs 15 normally position the armature 85 in the centerof the air gap of a magnetic core 81. The air gap is of sufiicient widthto permit the armature to freely oscillate within the gap when themagnet is energized. The energizing means includes the field coil 89,battery 9| and microphone 93. Amplifiers and lever actions may beemployed in place of the direct drive shown.

A modification of Figure VI is illustrated in Figure VII. The essentialdifference between the apparatus of Figure VI and Figure VII is that thelatter has a sound actuated diaphragm 95 to-actuate the magnetron withrespect to the non-uniform field. This field is produced by a magnetwhich has slanting pole pieces I9 similar to those shown in Figure We.

The diaphragm 95 may be a cone of suitable size. A flexible strip 9! ofleather or cloth connects the cone to a rigid supporting ring 99. Thecenter of the cone is connected to the movable end of the magnetron by alink IOI. Sound impressed on the diaphragm actuates the magnetron whichis pivotally mounted as previously described. This combination may beused as a microphone, microphone-amplifier, or oscillator, modulator andmicrophone.

In the embodiment of my invention shown in Figure VIII, the magnetron ismounted so that it may be rocked about the axis ofenvelope I. A pair ofmetal rings I03 are clamped at the ends of the envelope I. A pair ofwires I05 are attached to each of the rings. These pairs of wiresterminate in supports I01.

The pairs of wires and their connections act as a torsional balance. Thesuspended magnetron may be rocked about the axis of its envelope I. Inthis figure, the batteries and connecting' leads have been omitted. Themagnetron may be connected and adjusted for generating, amplifying,oscillating, or modulating currents.

The means for rocking the tube may bev a diaphragm, motor, or the like.For purposes of illustration, a sound actuated diaphragm 95 is shown.The diaphragm 95 is coupled to the envelope I. by suitable links IUI,I09. The force applied through these links rotates the magnetron aboutthe axis of envelope I. The field in the present instance is of theuniform type. Normally, the magnetic lines of force are substantiallyparallel to the cathode 3. As the magnetron is rocked back and forth,the relative angular relation between the electrodes, and the magneticlines is varied. This variation alters the electron flow and therebymodulates the output.

Thus I have described, and illustrated several embodiments of myinvention by means of which a magnetron may be used as a microphone,microphone-amplifier, modulated oscillator, a modulator, or audiofrequency generator. Various elements of each of the severalarrangements may be added to or substituted for elements of the othercombinations. For example, a diaphragm may be substituted for theelectromagnetic driving motors and vice versa.

I claim as my invention:

1. A magnetron including a cathode and anode electrodes, means forestablishing a magnetic field whose lines of force surround and aresubstantially parallel to said cathode and means for moving one of saidelectrodes in relation to said magnetic field in accordance with desiredsignals.

2. A magnetron including a cathode electrode and a pair of anodeelectrodes, means for maintaining a magnetic field whose lines of forcesurround and are substantially parallel to said cathode and means formoving said cathode electrode with respect to said anode electrodes inaccordance with desired signals.

3. A magnetron including a cathode electrode and spaced from saidelectrode a, pair of anode electrodes, means for creating a magneticfield whose lines of force surround and are substantially parallel tosaid cathode and an electromagneticmotor for varying the orientation ofsaid electrodes by relative motion of said electrodes.

4. A magnetron including a cathode electrode and spaced from saidelectrode a pair of anode electrodes, means for establishing a magneticfield whose lines of force surround and are substantially parallel tosaid cathode, and means for moving said electrodes with respect to saidfield for varying the operational characteristics of said magnetron at adesired rate.

5. A magnetron including an evacuated envelope having a rigid sectionand a flexible a section an electron. emissivecathode electrodesupported by one of said?sections; and agpair of anode electrodessupported by the othenof said sections; means .1 for-establishing a mag:

netic field to. thereby cause electrons emitted from said cathode ,totravelecurved paths to said anodes, and meansfor:flexingsaid'flexiblefsece Vtion sothat said cathodeand anodes-may-bemoved relative; toeachptherto thereby vary the number of electronstraveling-between said cath ode-and anodes. 1

- 6. A magnetrondncludingjan evaeuated ien 'velope having a rigidsection anda flexible metalliesection, an-electrorr emissivecathodeelec- 15 r for establishing amagnetic field to thereby cause electronsemitted from said cathode to travel:

curved paths to said anoclles,- andl'a pair of anode. v

trode supported by one of said sections, means electrodesl supported-by.the other of saidse'ccathodeand-anqd V 7.- Aj'jmagnetron including anevacuated envelope having a rigid section rand-a flexible section,a'cathode electrode supported by: one I of said sections, and a pair ofanode electrodes tions, jandrneans for flexing said metallic sec-V tl onsog -that said cathode and. anodes, may *moved relative to each, otherto' thereby vary the. number of electrons traveling'jbetween said 7supported by the :other of said sections,v .means' 7 for establishing a;magnetiefield' whose lines of force surround and are' substantiallyparallel to said" cathode, andlrmeans. for moving said flexiblesectio'ni in accordance with desired signals so that at least one ofsaid electrodes may be moved with respect tosaidmagnetiofield.

" o, ERNEST GJLINDER; V

